1. Field of the Invention
The present invention relates to the mounting of semiconductor devices using a film carrier.
2. Description of the Related Art
In general, semiconductor devices are manufactured by the following process: each semiconductor chip is mounted on a die pad provided on a lead frame; external electrodes of the semiconductor chip and the leads (terminals) of the lead frame are respectively connected to each other by means of a bonding wire; the assembly is packaged with a thermosetting resin such as epoxy resin; and the leads are trimmed.
In conjunction with the current trend toward thinner and more compact electronic units, with respect to semiconductor devices used in such units, efforts have been made to develop thin and compact semiconductor devices in order to realize the mounting of the semiconductor devices with a high mounting density. To meet this demand, semiconductor devices which have come to be used include semiconductor chips each disposed in a device hole of a film carrier, the electrodes of the semiconductor chip and the fingers of the film carrier are directly connected to each other, and this assembly is packaged with a sealing materials constituted by a liquid resin (e.g., epoxy resin) by printing or potting.
FIG. 7 is a top plan view illustrating a film carrier for semiconductor devices. A film carrier (hereinafter referred to as the film) 1 having a thickness of the order of 25-125 .mu.m is provided with device holes 2, 2a, 2b, . . . , each having an area larger than the surface area of an associated semiconductor chip 6, 6a, 6b, . . . , which will be described later, device holes 2, 2a, 2b being arranged at uniform intervals in the longitudinal direction of film 1. A multiplicity of fingers 3 are constituted by a metallic foil made of a material, such as copper, having a high electric conductivity and having a thickness of about 10-70 .mu.m and a width of about 30-300 .mu.m. Fingers 3 are disposed on film 1 and each finger 3 has a free end which projects into the associated device hole 2, 2a, 2b. Sprocket holes 5 are used to convey film 1.
FIG. 8 is a schematic diagram illustrating an example of an apparatus for mounting semiconductor chips on the above-described film 1. In operation, semiconductor chip 6 mounted on a pair of chip bases 8 is brought to a defined position by a pair of positioning guides 9. Meanwhile, film 1 is fed by means of a pair of sprockets (not shown) while being guided by a pair of tape rails 10 in a direction in which semiconductor chip 6 is fed. Film 1 is then stopped at a position where chip 6 is positioned below associated device hole 2. Subsequently, a multiplicity of pads 4 provided on semiconductor chip 6 and fingers 3 are respectively aligned with each other. Then, a heated bonding tool 11 is lowered to press fingers 3, so that fingers 3 are bent into a predetermined angle and are fused to respective pads 4 and connected thereto. Film 1 is then moved, and fingers 3 are trimmed, or fingers 3 are trimmed after semiconductor chip 6 and parts of fingers 3 are sealed with a sealing resin by means of squeeze printing, potting, or other similar method, thereby manufacturing a semiconductor device D.
As shown in FIGS. 9 and 10, the semiconductor device D manufactured as described above is mounted on a printed circuit board 20 with its active surface facing printed circuit board 20, after fingers 3 are respectively soldered to a conductive pattern 21 formed on a surface of printed circuit board 20, peripheral surfaces of semiconductor chip 6 and fingers 3 are sealed with a resin 12 or the like by means of squeeze printing, potting, or other similar method.
The printed circuit board 20 with the above-described semiconductor device D mounted thereon has characteristics that the printed circuit board 20 can be made thinner than a conventional one, and that the degree of mounting density can be increased. However, if the semiconductor device D is sealed with resin 12 or the like, a phenomenon occurs in which the printed circuit board 20 is curved or warped such that the side where the semiconductor devices D are mounted, assumes a concave curvature due to shrinkage upon curing of resin 12 or the like. This condition is depicted in FIG. 11.
Consequently, there are cases where compression cracks occur in semiconductor chip 6. In addition, if the curved printed circuit board 20 is secured to a frame or the like, the curvature must be removed. At that time, however, fingers 3 sealed with resin 12 or the like can be cut off, and, hence, there have been problems that the production yield is low and that such products lack reliability.
Furthermore, although the technique described above is capable of enhancing the degree of mounting density as compared with the conventional art, there are limitations to this, and it is considered difficult to improve the degree of mounting density by a substantial level in the future.